Paper pulp digester blowdown method

ABSTRACT

THIS INVENTION RELATES TO A METHOD OF MAINTAINING A CONTINUOUS BLOWDOWN FLOW OF PAPER PULP BETWEEN A PULP DIGESTER AND A HOT STOCK REFINER OR OTHER DOWNSTREAM EQUIPMENT COMPRISING THE STEPS OF PASSING DIGESTED PULP MATERIAL THROUGH A MODIFIED DIGESTER BLOW VALVE, TRAPPING LARGE, SOLID FOREGN OBJECTS THEREBY PREVENTING SAID OBJECTS FROM BECOMING LODGED IN THE ORIFICE OF SAID VALVE ROTATING THE BLOW VALVE, AND EXERTING A FLUID PRESSURE ON THE ORIFICE THUS BLOWING SAID FOREIGN OBJECTS INTO A BLOW TANK OR A TRASH BIN.

United States Patent 3,681,191 PAPER PULP DIGESTER BLOWDOWN METHOD FrankWilliams Farrelly, Merrick, N.Y., assignor to Process Evaluation andDevelopment Corporation, New York, N.Y.

Filed Nov. 10, 1970, Ser. No. 88,359 Int. Cl. D21c 7/08 US. Cl. 162-52Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method ofmaintaining a continuous blowdown flow of paper pulp between a pulpdigester and a hot stock refiner or other downstream equipmentcomprising the steps of passing digested pulp material through amodified digester blow valve, trapping large, solid foreign objectsthereby preventing said objects from becoming lodged in the orifice ofsaid valve rotating the blow valve, and exerting a fluid pressure on theorifice thus blowing said foreign objects into a blow tank or a trashbin.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to a method of conveying fluid pulp between a pulp digester andassociated downstream equipment such as a hot stock refiner, and moreparticularly to a method of maintaining a substantially continuous flowof fluid pulp between a pulp digester and the downstream equipment andthereby preventing the digester plug valve from becoming clogged byforeign material, and subsequently costly operation shutdowns.

Prior art The process of this invention is designed with particularreference to use in a system for conveying fluid pulp between acontinuous pulp digester and associated downstream equipment such as ahot stock refiner, although it can be adapted to various kinds ofsystems for conveying fluids from one vessel to another.

In the production of paper pulp from sugarcane bagasse or similarfibrous plant materials fibers are digested to produce pulp of a qualitysuitable for manufacture into paper. The digestion process includesdissolving the lignin, sugars, and resins content of the fibers, therebyseparating the cellulose from the cementing materials with as littledamage as possible to the cellulose. Problems arise due to the presenceof rocks and trash in the fiber feed to the pulp digesters. This foreignmaterial, after passing through the digester becomes clogged in thedigester blow valve causing many costly shutdowns.

The present invention eliminates the problems arising from foreignmaterial becoming clogged in the orifice of the digester blow valve, andprevents many costly opera tional shutdowns for the purpose of cleaningthe orifice.

SUMMARY OF THE INVENTION Generally speaking, this invention relates to amethod of maintaining a substantially continuous flow of fluid pulpbetween a pulp digester and associated downstream equipment such as ahot stock refiner, thereby preventing large, solid foreign objects frombecoming lodged in the orifice of the digester blow or blowdown valve,and subsequent operational shutdowns due to clogging.

The method of this invention comprises the steps of reducing thecross-sectional area of the valve flow path of the digester blow valveover a portion of the length of the said flow path; positioning thereduced orifice of the blow valve on the downstream side of the flow,thus pro- 3,681,191 Patented Aug. 1, 1972 viding a trap pocket in thepulp flow line between the digester discharge and subsequent processingequipment; passing digested material through the discharger and digesterblow valve, capturing large foreign objects in said trap pocket,rotating the reduced valve orifice so that the digester pressure isexerted on the opposite side of the reduced orifice, thus dischargingsaid foreign objects into a blow tank or into a by-pass line around thedownstream equipment and then into a blow tank, thereby clearing theplug; and returning said orifice to its original position therebyresuming normal flow of the digested pulp. It is also a variation ofthis invention to discharge the rocks or foreign materials into aseparate trash container by means of a stream or air jet.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the presentprocess of this invention may be best understood by reference to thefollowing description, taken in connection with the accompanyingdrawings, in which:

FIG. 1 is a schematic drawing of pulp digester and digester blow valve;

FIGS. 2 and 3 are more detailed elevational sectional views of thedigester blow valve of FIG. 1;

FIGS. 4, 5, 6 and 7 are elevational sectional views of a digester blowvalve used in the process of the invention embodying furthermodifications.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates pulp digester 10in which depithed fibers of sugarcane bagasse or similar fibrousmaterials are processed to separate the' fibrous constituents fromnonfibrous materials by dissolving the latter. When this process iscompleted, the digester contents are blown through discharger 11 anddigester blow valve 12 into the top of a blow tank where the digestedcontents are kept stirred by an agitator assembly and the stock ismaintained at a uniform consistency.

FIG. 2 illustrates an elevational, sectional view of a digester blowvalve 12 of FIG. 1, modified in accordance with the present invention,in its normal flow position. After the digester processes are completed,the digester contents are blown through inlet 14, and valve flow path 17including a reduced orifice 15 which has been sized for normal dischargefrom the digester. The material blown through reduced orifice 15continues through blow line 16 into the blow tank. When a large solidforeign object becomes lodged in orifice 15, clogging the digesterdischarge, valve flow path 17 is rotated 180 as shown in FIG. 3. Thedigester pressure exerted on the other side of orifice 15 blows the rockor foreign object into the blow tank thus clearing valve flow path 17.The flow path is then returned to its normal position illustrated inFIG. 2 and the blowdown process continued.

FIG. 4 is a sectional view of the digester blow valve 25 used in theprocess of this invention modified to operate when a hot stock refineris installed to further process digested pulp immediately after thedigester. Pressure of the digester forces the digested pulp throughinlet 20 and rotatable valve flow path 23 with a reduced orifice 21,then into the outlet flow path 22 leading to the hot stock refiner.Large, solid, foreign objects becoming lodged in reduced orifice 21,plugging the digester discharge, are removed by rotating valve flow path23, as shown in FIG. 5. The digester pressure now being exerted on theother side of reduced valve orifice 21 blows the rock or foreign objectthrough bypass outlet 24 into-the blow tank thus clearing valve flowpath 23. The reduced valve orifice 21 is then returned to its normalposition, and the blowdown process continued.

FIG. 6 is a sectional view of digester blow valve 31 of this inventionfurther modified to discharge foreign objects plugging the digester blowvalve into a separate trash bin. After the digester processes arecompleted, the digester contents are blown through inlet 26 androtatable valve flow path 28 with reduced orifice 27 which has beensized for normal discharge from the digester. The material blown throughsaid orifice 27 continues through blow line 32 into the hot stockrefiner. When a large solid foreign object becomes lodged in the reducedorifice 27, clogging the digester discharge, the valve flow path 28 isrotated 90 clockwise as shown in FIG. 7. By means of a live steam orpressurized air jet through line 29, the rocks or foreign materials areblown through outlet line 30 into a separate trash bin. The valve fiowpath 28 is then returned to its normal position illustrated in FIG. 6and the blow-down process continued.

It is apparent to those skilled in the art that various changes,modifications, additions and substitutions may be made in the methodsdescribed and structures illustrated herein without departing from thespirit and scope of the appended claims.

What is claimed is:

1. A method of maintaining a substantially continuous blowdown flow ofsolids contaminated paper pulp from a pulp digester discharge through adigester blowdown valve and then to a subsequent pulp processing vesselcomprising the steps of reducing the cross sectional size of the valveflow path of the digester blowdown valve over a portion of the length ofthe said flow path to form a reduced valve orifice in said flow path;positioning the reduced valve orifice on the downstream side of theblowdown flow thus providing a trap pocket in the valve flow path;passing the contaminated digested pulp material through the blowdownvalve; trapping solid foreign objects in said trap pocket; rotating theblowdown valve and '4 exerting a fluid pressure on the opposite side ofthe reduced valve orifice to discharge the trapped solid foreign objectsfrom the trap pocket and clear the valve flow path; and returning saidblowdown valve to its original flow position thereby resuming normalblowdown flow of the digested pulp.

2. The method of claim 1 wherein the valve is rotated so that thedigester blowdown pressure is the pressure exerted on the opposite sideof the reduced valve orifice to clear the valve flow path.

3. The method of claim 2 wherein the solid foreign objects aredischarged into a collecting tank or trash bin separate from thesubsequent pulp processing vessel.

4. The method of claim 1 wherein the fluid pressure exerted to dischargetrapped objects from the trap pocket is provided by pressurized steam orpressurized air flowing through the valve flow path when the valve isrotated out of its normal blowdown flow position.

5. The method of claim 4 wherein the solid foreign objects aredischarged into a collecting tank or trash 'bin separate from thesubsequent pulp processing vessel.

References Cited UNITED STATES PATENTS 3,486,516 12/1969 Stoertz 162-52X 2,115,675 4/1938 Tremmel 251209 X 2,621,012 12/1952 Graham 251207 X S.LEON BASHORE, Primary Examiner A. L. CORBIN, Assistant Examiner US. Cl.X.R.

